1. Field of the Invention
This invention relates to a legged mobile robot having a foot structure, more particularly to a legged mobile robot having a foot structure which increases the stability of the robot during walking.
2. Description of the Prior Art
Many improvements relating to legged walking mobile robots have been proposed. Improvements applicable to the autonomous biped type mobile walking robot can be found, for example, in Japanese Laid-open Patent Publication Nos. 62(1987)-97,005 and 62(1987)-97,006. Improvements relating specifically to the foot structure of the biped type mobile walking robot are disclosed in the assignee's Japanese Laid-open Patent Publication No. 3(1991)-184,781.
Among the different types of mobile walking robots, the biped walking type robot is by nature the most unstable. Depending on the conditions of the ground or other surface the robot walks over, the walking environment, the walking speed and the like, it is often difficult to maintain the robot stable during walking. Although it is relatively easy for the robot to maintain its stability during low-speed walking on a flat horizontal surface, the biped walking robot tends to become unstable under various unusual circumstances, as during stair climbing and descent, walking on an inclined surface, walking over a surface with obstacles, and walking at high speed. Biped walking may also be made difficult by external environmental factors such as earthquake-induced vibration and the wind.
One conceivable way of increasing the stability of a biped walking type legged robot during walking is to design the robot's feet to have a large ground contact surface, i.e. a large surface for making contact with the terrain. Depending on the walking conditions, however, simply making the feet larger may have the opposite effect of destabilizing the robot. For example, when a robot with big feet climbs stairs, the toes of its feet are apt to catch on the step overhangs that are usually provided on stairs. When this happens, there is a high likelihood of the robot falling over. Moreover, when a robot steps over a projection or other such obstacle on the terrain, the likelihood of its falling over because the toe or heel portion of the foot comes in contact with the obstacle is greater if its feet are large. On the other hand, during fast walking there is a greater possibility of interference between the feet and resulting tip over if the feet are large. While there are also many other circumstances in which large feet tend to detract from the walking stability, those mentioned in the foregoing are sufficient to show that simply making a robot's feet larger does not provide a basic solution to the problem of how to increase stability during walking.